Frank and Jared are aiming to have the Australis theme up for review next week in bug 732583. There are no computed borders or gradients in the redesign, so it will be faster. The current theme generates new borders/gradients on every tab interaction, which is very inefficient. Bas is working on fixing our graphics backend to render borders/gradients more efficiently in bug 750871.
Wlad spotted some unintended bloat in the addon database in bug 752868. Blair fixed it, this should speed up startup and other addon manager interactions.
We started a new project to let Firefox diagnose common Windows/etc misconfiguration issues that severely impact Firefox performance. Our new intern, Nicholas, is working on this in bug 684646. The immediate plan is to release an addon that detects when Firefox startup is unusually slow, checks for known Windows issues and pops up a link to a Mozilla support article on how to fix the problem. If this turns out to be successful, we’ll integrate this functionality into Firefox.
The gecko profiler is now ready for general consumption. See Benoit’s announcement. This will allow users running the profiling variant of Firefox nightly builds to capture/report performance problems in a way that developers can act on. I suspect that Benoit will blog about this.
Update: I originally linked the wrong bug for windows misconfiguration detection.